There are various medical applications for such methods and equipment. One of these applications is for intraoperative autotransfusion, which has been widely used in recent times. Intraoperative autotransfusion is a method which permits retransfusion of blood collected from the surgical field. What are known as whole-blood transfusion methods, which subject the collected blood to particle filtration only, are used in the area of intraoperative autotransfusion to the point of plasma separation/washing methods which supply a washed RBC concentrate for reinfusion. The advantages of transfusion of autologous blood, i.e., the patient's own blood, in comparison with transfusion of homologous blood, i.e., someone else's blood, include the prevention of infectious diseases such as AIDS and hepatitis as well as the prevention of transfusion reactions due to biological incompatibility and immune system reactions.
As part of the development of intraoperative autotransfusion techniques, it has been found that transfusion of whole blood may be a disadvantage in comparison with transfusion of washed RBC concentrates. These disadvantages of the whole blood transfusion methods include the fact that undesirable components of the collected blood cannot be eliminated. Intraoperative blood contains unknown quantities of hemolysis products, foreign constituents infiltrated from the tissue or from external sources, excess volume, anticoagulants, activated plasma and cellular coagulation factors, products of the activation of coagulation and products of the fibrinolytic system. All these components can cause clinical complications, which has led to restrictions on the scope of use. It is known from the related art that blood filtering systems can be used with such autotransfusion systems, but these filters retain only blood clots or pieces of tissue. Such a system is known from U.S. Pat. No. 4,014,329. U.S. Pat. No. 4,886,487 describes an apparatus for separating excess fluids, but coagulation factors, washing fluid, anticoagulants and other additives are returned with the patient's blood.
As an alternative to whole-blood transfusion, phase separation/washing methods using centrifuges have been developed. Such centrifuges are described in Unexamined German Patent No. 2,262,856 and International Patent WO 89/01792.
German Patent No. 3,817,664 describes a countercurrent extraction centrifuge, in which whole blood is carried in countercurrent with a wash solution. However, neither this apparatus nor this method meets the requirements demanded for autotransfusion, because the unwanted components cannot be separated reliably and effectively.
German Patent No. 4,226,974 C2 describes a method of processing intraoperative blood loss, in which the cell suspension to be processed is passed through a centrifuge line into a separation chamber, where it is broken down into its components according to density. In a second process step, the concentrated cell fraction, mainly RBC concentrate, is resuspended by continuous addition of a wash solution. Then the remaining noncellular components are subjected to another separation, yielding a high-purity RBC concentrate after removal of the contaminated wash solution. A centrifuge with a separation chamber having an annular channel is used to carry out the process. The annular channel is divided into three zones, with the first separation of the cell suspension taking place in the first zone, resuspension in the second zone and the second separation of the resuspended cells in the third zone.
The above method has proven successful in practice, but it has the disadvantage that relatively large volumes of wash solution must be passed through the centrifuge chamber to displace or dilute the remaining plasma. In view of the large tS volumes, an isotonic saline solution is generally used as the wash solution in the known method. Because of the relatively large volumes involved, using Ringer's solution, which is tolerated much better by the patient, instead of saline solution is associated with a relatively high cost because the Ringer's solution is more expensive.